The Evolution Underground

Humans have "gone underground" for survival for thousands of years, from underground cities in Turkey to Cold War-era bunkers. But our burrowing roots go back to the very beginnings of animal life on Earth. Many animal lineages alive now--including our own--only survived a cataclysmic meteorite strike 65 million years ago because they went underground.

On a grander scale, the chemistry of the planet itself had already been transformed many millions of years earlier by the first animal burrow...